Power controllers have been provided to limit the power delivered to a load, thereby protecting it from thermal failure or other damage. See, for example, U.S. Pat. No. 6,141,197, providing a smart circuit breaker for residential use, U.S. Pat. No. 6,836,099, providing a power controller for real-time monitoring and adjustment of power usage by the load, U.S. Pat. No. 6,704,181, providing an adaptive power controller that dynamically controls the power based on information received from the load, and U.S. Pat. No. 6,122,180, providing a constant power controller for maintaining a constant power to the load.
In particular, constant power controllers monitor the power delivered to the load such that the power may not exceed a predetermined power level for some programmable amount of time. Such power level may be the constant maximum value permitted by the load and set by the load manufacturer to comply with its safety restrictions. In typical implementations, an adaptive trip threshold may be used to indicate when to trip off power to the load. Usually it is desirable to implement the adaptive trip threshold transfer function with accuracy less than +/−2%. Realization of such transfer function prevents excessive losses of power without violating the safety restrictions of the load.
There remains, however, a need to implement this transfer function with higher accuracy and with a relatively simple power controller circuit.